Wavelength division multiplexed (WDM) optical communication systems are known in which multiple optical transmitters supply each of a corresponding one of a plurality of modulated optical signals. The optical signals may be combined by an optical combiner or multiplexer in a transmit node and supplied to an end of an optical communication path. The combined optical signals may then propagate along the optical communication path to a receive node, where the optical signals are demultiplexed and each is supplied to a corresponding optical receiver.
Each optical transmitter may include a laser that outputs light having a particular wavelength and a modulator that modulates the light in accordance with a data stream to provide a respective one of the modulated optical signals. Other optical components may also be provided. Typically, optical fibers or other waveguides are provided to direct light from one component to the next, e.g., from the laser to the modulator, and from the modulator to the combiner. An interface may exist between an end face of the fiber and part of the component that receives the light. Light may scatter at such interfaces, and such scattered light may be fed back to the laser and interfere with the operation of the laser. Alternatively, the scattered light may interfere with optical signals propagating in the waveguides. Often the waveguides are tilted or angled in such a way as to reduce such scattering back into the source waveguides and the lasers whereby the waveguide may “dodge” the scattered light.
In another example, the optical combiners or couplers may include a portion through which unwanted portions of the combined optical signals may escape. Such light may also constitute undesired feedback to the lasers as well as interfere with optical signals propagating in the waveguides. Accordingly, additional waveguides may be provided at such “dump ports” to direct the undesired light away from waveguides carrying optical signals and the lasers.
Conventional WDM optical communication systems often include discrete components, such that, for example, the lasers, modulators, and other components are housed separately from one another or provided on separate substrates. Other WDM optical communication systems, however, include photonic integrated circuits (PICs) in which these components may be integrated on a common substrate. As the density and size of PICs increases, the conventional approaches to reducing scattered light may be impractical due to the layout or configuration of various components on the PIC.
Accordingly, there is a need for devices that can be readily integrated on a PIC and reduce unwanted light.